Power plants and other facilities with fluid purification processes frequently have used filter tanks or filter vessels to purify a variety of different liquids or gases, such as fluid fossil fuels, steam or water. Such filter vessels have an inlet supplying a fluid to a main filtration chamber holding a number of tubular filters. Long tubes within the filter vessel support and act as the core for the tubular filters. These long tubes extend from a tube sheet that separates the main chamber from a plenum for holding purified fluid. An outlet leads from the plenum to the exterior of the filter vessel.
In conventional practice, on the opposite end of the filters from the tube sheet, separate filter mount assemblies secure the filters to the tubes while sealing that end of the tube. The conventional filter mount assemblies contain numerous parts, which frequently fall into the filter vessel during disassembly of the mount assembly to replace the filters. Parts falling into the vessel must be removed to prevent damage to filter elements caused by motion of the loose parts during service flow. If loose parts cannot be readily located and removed with suitable “fishing” tools, filter elements must be removed to permit access to the vessel to retrieve the loose parts. U.S. Pat. No. 5,667,679 to Bozenmayer et al. attempts to solve this problem by providing a filter mount assembly that may be removed quickly without losing parts. This design, however, uses stainless steel parts that are difficult to dispose or recycle when radioactive, which condition may obtain in nuclear power plants.
Another problem associated with conventional filter mount assemblies relates to the ease of installation and removal. Rapid installation and removal of filter elements in radioactive steam systems or other hazardous environments is highly desirable to minimize worker exposure.
Referring to FIG. 1, another conventional filter vessel 100 has an inlet 102 that delivers unpurified, typically pressurized, fluids to a main chamber 104. The arrows F indicate direction of flow for the fluid during normal operations.
The fluid enters replaceable filter cartridges 106, as known in the art, and through known tubular filters contained thereby that remove unwanted particulate or foreign matter. The purified fluid then flows downward through tubes or pipes 108 that open up into a plenum 110. The plenum is separated from the main chamber 104 by a stainless steel or a carbon steel false bottom or tube sheet 112 conventionally welded to the tubes 108. The fluid then exits the filter vessel 100 through an outlet 114. Conventional filter vessels 100 typically vary in diameter from six inches to seven feet (and three foot to eight foot heights) depending on the quantity and size of filter elements contained therein. Vessels are known to accommodate anywhere from two to over 1000 filter cartridges.
Some conventional filter cartridges 106 are held in place by a hold down plate 116 as known in the art. The filter cartridges 106 are single open-ended with a closed top and a protruding bolt, post, rod or other connector 118 to extend upward through a hole in the hold down plate 116 for lateral support and to maintain distances between adjacent filter cartridges. The hold down plates 116 are usually bolted to the perimeter of the vessel or secured to the bottom by long connecting rods (not shown). Either mechanism provides downward force to seal the cartridges 106 to the tube sheet 112. Cartridges 106 that are held down by hold down plates 116 typically have a spigot that fits into holes in the tube sheet 112, and is sealed with either a flat gasket or one or more O-rings (not shown).
Some filter cartridges 106 have threaded bottoms for securing the filter cartridge to the tube sheet 112 and effecting a liquid tight seal, and these therefore do not require a hold down plate. However, threading of the filter cartridge 106 onto each of the tubes 108 requires numerous rotations of the filter cartridge 106 by a robot, hand, wrench, other special tool or automatic mechanism. The threading and unthreading of the filter cartridge 106 is a time consuming job which undesirably prolongs the worker's exposure to a hostile environment.
U.S. Pat. No. 3,279,608 to Soriente et al. discloses a guide rod and hook design used to mount a filter cartridge onto a tube welded to a tube sheet such as an Aegis™ Fossil Assembly as is known in the art. The filter cartridge has a guide rod welded to a plate with an end having a hook. A coil spring and nut are used to seal the top of the filter while compressing the filter cartridge against the tube to hold it in place against an adapter threaded permanently to the tube.
The upper end of the guide rod is used to attach to a positioning lattice for lateral stabilization. This design, however, still requires the unthreading of the nut to remove the filter cartridge from the tube, and the rivet hook is not considered to be of adequate strength for high pressure and highly corrosive nuclear power plant applications.
Another known filter cartridge and filter vessel eliminates the need for threading the filter cartridge to a tube on a tube sheet. As shown on FIGS. 2A-2D, a filter cartridge 500 has a steel adapter 502 that connects a filter 504 to a stainless steel filter vessel tube 506. As shown in FIGS. 2C-2D, a spring 508 applying forces of 50-60 pounds is located between a support ring 510 welded to the exterior of the tube 506 and two pins 512 also welded to the exterior of the tube 506. Referring to FIGS. 2B and 2C, the adapter 502 has two opposing slots 514 (only one shown) for receiving the pins 512 and has an annular groove 516 that slides over the pins 512 as the adapter 502 is rotated about the tube 506. Once the adapter is rotated 90°, as shown in FIG. 2D, the pins 512 are positioned in two opposing locking apertures 518.
In order to position a filter cartridge 500 on the tube 506, the filter cartridge must be pushed downward (axially) to engage the pins 512 and spring 508, and then rotated a full ninety degrees to place the pins 512 in the locking apertures 518. The spring 508 biases the adapter 502 upward to hold the pins 512 against the bottoms 520 of the locking apertures 518, which further stabilizes and secures the filter cartridge 500 on the tube 506.
In some nuclear power plant filter vessel applications, during backwashing (fluid flow in the upward direction on FIGS. 2A-2D) the spring and fluid can combine to form an axial force of over 100 pounds that impacts the filter cartridge 500. The adapter 502 must be made of steel to withstand this force, which is transmitted through the circular pins 512. Otherwise, the high axial forces will cause the pins 512 to rip through an adapter 502 made of a weaker material, such as plastic, and disengage the filter cartridge 500 during backwashing operations.
Radioactive steel hardware, however, is dangerous, difficult and expensive to handle when replacing filter cartridges. Steel hardware cannot be recycled or incinerated using present technology. Re-use of the hardware with new filter cartridges is not practical due to the amount of radiation to which the operator is exposed. For this reason alone, the hardware is often replaced rather than re-used. The discarded hardware that is disposed of as radioactive waste will incur a disposal cost that is ten times or more its initial cost.
Accordingly, what is needed is an inexpensive, easy to use filter mount assembly constructed of easily and economically disposable materials.